The US Computer Emergency Response Team (US-Cert) is warning users and administrators to be on the lookout following the discovery of a malware outbreak being spread via USB keys.

The rise in attacks was first reported by researchers at Symantec, who noted that the attacks are taking two principal forms.

The first tactic involves malware which simply copies itself to all storage devices connected to the infected PC. This tried-and-true method is usually delivered by way of social engineering, often posing as video or application files.

The second method uses the Autorun feature in Windows. The malware copies itself from the infected machine onto a USB drive as 'autorun.inf', allowing the file to execute automatically and perform a new infection when the drive is plugged into another system with Autorun enabled.

USB drive attacks use methods as old as the computer virus itself, early versions of which spread by infecting floppy disks and local networks.

The tactic eventually gave way to web page and email borne attacks, but Symantec suggested that the increasing use of media players and USB drives is making the tactic popular once again.

In order to avoid attacks, US-Cert recommends that users and administrators disable Autorun for connected devices. Symantec also suggests setting policies which limit the ability of users to connect USB devices unless absolutely necessary.